1. Field of Invention
The invention relates to a device for triggering an event in phase with an angular position of a component driven to execute a rotary movement.
2. Prior Art
Such a device is used, in particular on internal-combustion engines having electronic ignition to ignite, at a particular point of the engine cycle, the explosive mixture compressed within a cylinder, that is to say with an angle of advance determined in relation to the passage of the piston through the top dead center. To this end, it is known to register the angular position of the crankshaft by means of a disc or target which is rotationally connected to the crankshaft and provided, at its periphery, with a series of registration marks passing in front of a sensor which may be of the magnetic, capacitive, optical or some other type.
U.S. Pat. No. 4,321,580 describes a device in which the disc comprises, at its periphery, a succession of teeth and of recesses which are regularly spaced and one or more discontinuities constituting absolute registration marks. The discontinuities may be formed by longer teeth and/or missing teeth. After shaping, the output signal of the sensor is applied to a specific electronic circuit which delivers a certain number of signals, that is to say:
a rectangular tooth signal which is the image of the succession of the teeth and of the recesses at the periphery of the target;
an interpolation signal which is formed by a series of pulses representing the division of the angular interval between two teeth into equal angular fractions;
a synchronizing signal formed of pulses which coincide with the discontinuities of the disc or are phase-shifted by a predetermined angle in relation to said discontinuities, for example in order to identify the top dead center of the pistons.
As described in U.S. Pat. Nos. 4,367,710 and 4,469,081 these signals may be used by a computer which determines the angle of ignition advance as a function of the operating parameters of the engine, and the output stage of which controls the placing of the coil in a conductive condition and its discharge causing the ignition spark. In order to obtain the triggering of the spark, a counter is preloaded with the calculated value of the angle of ignition advance, expressed as the number of pulses of the interpolation signal. This preloading, possibly supplemented by a fixed number if the maximum capacity of the counter exceeds the number of pulses of the interpolation signal between two synchronizing signals, is ensured by the ignition computer under the control of the synchronizing signal. The preloaded counter is then incremented on its most significant inputs by the tooth signal until all its most significant outputs are in the "1" condition. A set of logic gates then permits incrementation of the least significant inputs of the counter by the interpolation signal. When all the least significant outputs are likewise in the "1" condition, that is to say when the counter runs over, the ignition is triggered.
Although operating satisfactorily in the application considered, this device for triggering an event by a counter with preloading does nevertheless involve certain constraints which limit the possibilities thereof.
Thus, a single counter with preloading will be able to ensure the triggering only of a single type of event, for example the ignition, and it will be necessary to provide as many counters with preloading as there are events of different types of events to be triggered.
On the other hand, the actual process of triggering an event in phase with an angular position of the crankshaft is such that the computer must preload the counter at the moment when the synchronizing signal appears. This synchronization of the preloading with the engine cycle is detrimental to the optimal utilization of the computer, the computing speed of which is constant, while the periodicity of the synchronizing signals is a function of the speed of rotation of the engine which varies from a few tens of revolutions per minute in the course of cold starting to several thousand revolutions per minute at maximum speed. If other functions such as the detection of knocking in an angular window situated close to top dead center, the correction of knocking (possibly cylinder by cylinder) the computation of the injection time and the control of the injectors, the regulation of idling, the driving of an automatic gearbox, the control of the opening time of the valves, etc . . . are likewise to be ensured (certain ones of these functions themselves possibly necessitating the triggering of events in phase with the engine and thus aggravating the problem), it will be difficult to cause these to coexist within a single computer. It will then be necessary either to distribute these functions among a plurality of computers, or to use a faster computer which will in reality be of excessive size as compared with what would be strictly necessary for the performance of the computations, setting aside the interruptions which are necessitated by the preloading of the counter or counters for triggering events. In both cases, the cost of the electronics is increased.